1. Field of the Invention
The present invention relates to an illuminating optical system and an image display apparatus using the same, and more particularly, to highly efficient illuminating optical system with high optical efficiency, an image display apparatus using the same, and an image display method.
2. Description of the Related Art
Projection type image display apparatuses focus light emitted from a light source on a microdisplay, that is, a light valve such as, for example, a liquid crystal display (LCD) or a digital microdisplay (DMD) and control the light on a pixel-by-pixel basis, thereby forming an image. The formed image is magnified and projected on a screen using a projection optical device, thereby providing a wide picture.
In the image display apparatuses, brightness of an image depends on the intensity of light condensed on the light valve.
A conventional illuminating optical system typically includes a fly eye lens or a glass rod for efficiently condensing light emitted from a lamp light source on a rectangular shaped light valve.
The aforementioned conventional illuminating optical system is not without problems. For example, when using the lamp light source as a light source, light emitted from the lamp light source is incident on the fly eye lens or the glass rod without changing the shape of the light, thereby reducing optical efficiency. More specifically, while circular light is emitted from the lamp light source, the fly eye lens or the glass rod has a rectangular shape corresponding to the rectangular shaped light valve. Thus, when the circular light emitted from the lamp light source is incident on the rectangular shaped fly eye lens or the glass rod, light loss is caused due to a difference in shapes.
For example, light emitted from the lamp light source passes through a first fly eye lens, and then is formed as a light spot on a second fly eye lens. If a size of the light spot is larger than that of the second fly eye lens, the portion beyond the size of the second fly eye lens is lost, thereby reducing the optical efficiency.
Further, if the light spot formed by the first fly eye lens is not beyond the second fly eye lens, the power of the first fly eye lens must increase and a distance between the first fly eye lens and the second fly eye lens must be short. However, in this case, an effective area of the light valve is reduced. If the effective area of the light valve is reduced, condensing light on the light valve is difficult, thereby reducing the optical efficiency.